Aluminium-based article having a protective ceramic coating, and a method of producing it

Abstract

Described are an aluminium-based article having a heat and corrosion protective coating, especially engine parts such as piston crown or cylinder head, and a method of preparing said article. The coating consists of an aluminium-based bonding layer, preferably having a thickness in the range 0.1-0.6 mm, and an outer top layer of stabilized or partially stabilized zirconium dioxide, preferably having a thickness in the range 0.5-2.5 mm, and optionally a cermet layer, comprising zirconium dioxide and an aluminium-based metal component, between the bonding layer and the outer zirconium dioxide top layer. The bonding layer is applied to the substrate by thermal spraying of a rapidly solidified powder, substantially consisting of 60-80% by weight of Al and 40-20% by weight of Si, the particles of the powder having a frozen unstable micro-structure. The cermet layer desirably is a layer consisting of zirconium dioxide and an aluminium-based alloy, the metal content of the cermet layer decreasing substantially uniformly in the direction towards the outer zirconium dioxide top layer. The cermet layer preferably has a thickness in the range 0.2-0.6 mm. Also the cermet and zirconium oxide layers are deposited by thermal spraying.

I claim: 
     
       1. An aluminum-based article having a heat and corrosion protective coating on at least a portion thereof, said coating comprising a bonding layer applied to said article by plasma spraying of a rapidly solidified Al-Si-based powder comprising from about 60% to about 80% by weight of Al and from about 40% to about 20% by weight of Si, and an outer top layer of stabilized or partially stabilized zirconium dioxide. 
     
     
       2. The article according to claim 1, wherein a cermet layer comprising zirconium dioxide and an aluminum-based metal component is provided between the bonding layer and the outer zirconium dioxide top layer. 
     
     
       3. The article according to claim 2, wherein the cermet layer is a layer consisting essentially of zirconium dioxide and an aluminum-based alloy, and wherein the metal ratio of the cermet layer decreases substantially uniformly in the direction towards the outer zirconium dioxide top layer, and zirconium dioxide ratio of the cermet layer increasing from 0 to 100% zirconium dioxide at the transition into the outer top layer. 
     
     
       4. A method of providing an aluminum-based article, with a heat and corrosion protective coating, comprising steps of applying to at least a portion of the surface of said article, a bonding layer by plasma spraying of a rapidly solidified Al-Si-based powder comprising from about 60% to about 80% by weight of Al and from about 40% to about 20% by weight of Si, and providing an outer top layer of stabilized or partially stabilized zirconium dioxide on top of at least a portion of said bonding layer. 
     
     
       5. A method of providing a piston crown or cylinder head, with a heat and corrosion protective coating, comprising steps of applying to at least a portion of the surface of said piston crown or cylinder head, a bonding layer produced by plasma spraying a rapidly solidified Al-Si-based powder comprising from about 60% to about 80% by weight of Al and from about 40% to about 20% by weight of Si, applying to at least a portion of said bonding layer a cermet layer comprising zirconium dioxide and an aluminum-based metal component, and providing an outer top layer of stabilized or partially stabilized zirconium dioxide on top of at least a portion of said cermet layer. 
     
     
       6. The method according to claim 5, wherein said cermet layer is a layer consisting essentially of zirconium dioxide and an aluminum-based alloy, said cermet layer having a substantially uniformly decreasing metallic proportion in the direction towards the outer zirconium dioxide top layer, the zirconium dioxide proportion of the cermet layer increasing from zero at the innermost portion to 100% zirconium dioxide at the transition into the outer top layer.